1. Field of the Invention
The present invention relates to a counter device comprising a master counter and a plurality of functional blocks each including a local counter.
2. Description of the Prior Art
An increase in the packing density of LSIs increases power consumption in wiring, thus exerting a large influence upon the power consumption in the whole of one chip. In one-chip devices, such as system LSIs, including a plurality of functional blocks, the length of wiring for connecting them with each other increases with increases in the number of the plurality of functional blocks. It is thus important to reduce power consumption in wiring through which a signal to be referred in common by the plurality of functional blocks is passed.
System LSIs have a plurality of blocks formed in units of functionality and a common time to cause the plurality of functional blocks to operation in cooperation with one another. For example, in a system which conforms to the Read-only DVD Standard, a plurality of decoders (for Video Sub-picture, PCI, Audio) can refer to System Time Clock or STC. The STC is a timer whose value periodically varies.
When each of a plurality of blocks refers to STC within one chip device in which a master counter is provided for enabling each of the plurality of blocks to refer to the STC, as shown in FIG. 5, that is, each of the plurality of blocks refers to the contents of the master counter, a bus connecting the master counter with the plurality of blocks frequently changes in voltage, thus increasing the power consumption in the bus.
Referring now to FIG. 6, there is illustrated a block diagram of another prior art counter device in which a plurality of functional blocks include respective counters that can be brought into synchronization with each other by a common control signal (or reset signal). The prior art counter device can reduce the power consumption because it does not include a bus for connecting a master counter with the plurality of functional blocks. However, since each of the plurality of functional blocks needs its own counter, the amount of hardware is increased.
A problem with a prior art counter device as shown in FIG. 5 is that each of a plurality of functional blocks needs to refer to a master counter, such as a timer counter, whose count value periodically, frequently changes, and therefore a bus for connecting the master counter with the plurality of blocks frequently changes in voltage or value, thus increasing the power consumption. Further, a problem with another prior art counter device, as shown in FIG. 6, in which a plurality of functional blocks include respective counters, is that although the power consumption can be reduced because no bus is needed for connecting a master counter with the plurality of functional blocks, the amount of hardware is increased.